A Glossary of Speaker Materials

What to look for when you're shopping for speakers

A

Aluminum-coated polypropylene
Polypropylene coated with a thin layer of aluminum. The combination creates a stiff, lightweight material used in woofer cones.

Aramid
A synthetic fiber with excellent strength-to-weight properties. It can be woven into a fabric, or blended into polypropylene to produce lightweight, weather-resistant woofer cones that have the natural sound characteristics found in high-quality paper cones.

B

C

Cast aluminum
Cast metals have a greater resistance to resonance than stamped metals when used in speaker baskets. Cast aluminum combines light weight with rigidity and strength.

C.M.M.D. (Ceramic Metal Matrix Diaphragm)
First developed by Infinity for their home speakers, C.M.M.D. is a layered composite of thin ceramics and metal. This material is non-resonant, stiff and quite strong. It is notable for producing uncolored sound with excellent dispersion. C.M.M.D. is used for woofers, midranges and tweeters.

D

E

F

Ferrofluids
Ferrofluids dissipate heat that builds up in speaker voice coils. Since ferrofluids are magnetic, they don't require physical containment — the speaker's magnetic field holds the fluid in place.

Foamed IMPP
When polypropylene is injected as a foam into a speaker mold, the resulting material retains air bubbles that make it lighter without giving up strength.

H

HCL
HCL (HoneyComb-Laminate) is a laminate that combines layers of woven glass fiber with an inner core of Nomex honeycomb. The result is a very strong material, excellent for speakers that need to handle high power.

H.O.P. (Highly Oriented Polyolefine)
The molecules in Highly Oriented Polyolefine are arranged in linear strands, giving this material more inherent strength and rigidity than most other polymer films. H.O.P. is used by Sony for woofer cones.

I

IMPP (injection-molded polypropylene)
IMPP consists of polypropylene that is injected into a mold when forming the speaker cone. The speaker cone retains more stiffness, and is less colored by resonation, than cast polypropylene cones.

IMPP composite
To increase the strength and stiffness of IMPP, other materials are added to form IMPP composites. These materials are usually minerals like mica or carbon.

J

K

Kaladex/Kaladax
A polyethylene film that features excellent stiffness, shape retention, and durability. Tweeters made with this material produce natural, uncolored highs.

Kapton voice coil
Kapton is a polymer that is often used in applications where high-temperature capabilities are important. It's well-suited for use in voice coil formers.

Kevlar®
Kevlar is the trademarked name of a synthetic fiber developed by DuPont as a substitute for steel in tires. Also used in body armor, Kevlar, blended with other polymers, is used in speaker cones for its light weight, strength, and rigidity.

L

M

Mylar
Mylar, developed in the 1950s, is one of the granddaddies of polyester films. Mylar is usually used in small speakers such as tweeters or midranges. It's unaffected by humidity and is fairly inexpensive. Also known as PET.

O

P

PBO fiber
PBO (polybenzoxozole) is a polymer that can be extruded into fibers and woven into a tough material. This fiber is used to build woofer cones.

Pearl polycarbon
Polycarbonates are blends of polyester films and carbon. Pearl polycarbon is a very lightweight yet rigid material that works well in tweeters. Pearl refers to the bead-like microscopic structure of the polymer.

Pearl mica
Micas are a group of minerals composed of various amounts of aluminum, potassium, and other metals. Pearl mica has a distinct lustrous, pearl-like color. When injected into polypropylene, it yields a material that is dense yet sensitive — ideal for woofer cones.

PEI
See Polyetherimide.

PET
A generic name for Mylar.

Polyethylene
A polymer film material used in tweeters. Very similar in performance to Mylar.

Poly
See "Polypropylene"

Polycarbonate
A blend of polyester films and carbon resulting in a hard, non-resonant material used mainly in bright-sounding tweeters, and occasionally in constructing the speaker basket. Polycarbonates can be produced in a variety of colors, including transparent, for a distinctive look.

Polyester foam
Foam material with polyester fibers blended for extra strength and durability. Polyester foam is used for speaker surrounds.

Polyethermide
See Polyetherimide.

Polyetherimide
Polyetherimide, also known as PEI, Polyethermide, or Polyimide, is a very common polymer used for a variety of products. Its lightweight, shape-retaining properties, and high-temperature handling make it a good, reasonably-priced option for tweeter material.

Polyimide
See Polyetherimide.

Polymer/mica
A polymer film, such as polypropylene, made stronger by the addition of the mineral mica.

Polypropylene
A very popular material for car speakers, polypropylene is fairly rigid, with good internal damping, and complete weather-resistance.

PPC
See "Pearl polycarbon."

PPTA
A polymer film that is chemically the same as "Aramid," but produced as a film, rather than as a fiber. It has the same excellent strength-to-weight characteristics as Aramid, and is usually used in tweeters and midranges.

Pulp
Pulp (paper) woofers are inexpensive, and when properly engineered can provide great sound. However, they're rarely used in car speakers because of susceptibility to moisture.

Q

R

S

Silk
They don't say "smooth as silk" for nothing. Silk is a highly-regarded material for tweeters because of the smooth, open, and airy sound it produces. For best performance, it must be properly treated and coated. High-quality silk can be somewhat expensive.

Silk/polymer composite
Silk is blended with polymer materials to create a strong, rugged composite used in tweeters.

Silver film
Used as a thin coating over polymer materials like PET, silver film provides a brighter sound than the polymer alone. This material is used in tweeters.

Strontium magnet
A rare earth metal which is used in creating small, high-strength magnets. A small, strong magnet is very useful in building an effective tweeter.

U

UFLC
UFLC is the abbreviation for "polyUrethane Film Laminated Cloth." This material is used in soft dome tweeters because of its light weight, ability to keep its shape, and smooth, natural sound characteristics.

Urethane
Urethane is a plastic compound that's more flexible and weather-resistant than natural rubber. This compound is used for making speaker surrounds.

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Crutchfield Writer Biography

Ken Nail

Ken Nail has written about car audio for Crutchfield since 2003, after four years as Crutchfield Sales Advisor, and 10 years as a music teacher. He's an avid music listener, whose favorites are classical and film music. When not chained to a desk, Ken spends most of his time training for triathlons and marathons, and likes getting outside for backpacking, downhill skiing, and bicycle touring. He attended West Virginia University, where he received a Master's Degree in Music Performance and a Bachelor's Degree in History.